The thermal energy materials and systems group is working to model and design efficient energy technologies which can be used to reduce energy consumption in buildings. Materials that can be used for thermal storage and better thermal management of electronics systems used in buildings are being developed. The implementation of modeling approaches from the component level to the system level via Energy Plus allows for performance evaluation of these technologies in different internal and external conditions. This group is working with a large group of collaborators including Colorado School of Mines, Oak Ridge National Laboratories, National Renewable Energy Laboratories, Lawrence Berkeley National Laboratories, and groups from the Army and Navy to reduce energy consumption in military as well as non-military buildings. Technologies under evaluation are thermal energy storage materials, solid state and plasma lighting, HVAC, and dynamic window systems.
Thermal Energy Storage (Georgia Tech, Oak Ridge National Laboratory
Latent heat thermal storage systems comprise one technology to create “thermal batteries” critical for waste heat energy harvesting and solar thermal technologies. Waxes and bio-derived phase change materials are being considered for this application due to their high latent heat thermal storage capability. However, the rate at which thermal energy flows into and out of wax system is limited in part by the characteristic low thermal conductivity. To improve the rate of thermal energy storage or “power” of the thermal battery, we are investigating the fabrication of phase change composites and foams infiltrated with phase change materials to improve their thermal performance.
We have utilized techniques such as integrating graphite nanoplatelets to improve the thermal conductivity of wax materials. While improvements in thermal conductivity can be found, the particles settle out when the wax is in the liquid state as seen in Figure 1. Through the use of chemical bonding groups, it is possible to keep platelets as large as 15 mm suspended in the liquid state and maintain the uniformity in thermal conductivity of the system*. Additional efforts to improve the thermal energy storage and discharge rates have come through the use of both aluminum and compressed expanded graphite foams shown in Figure 2. These materials are being used to design and model the performance of thermal storage systems.
*Anne Mallow, et al., “Investigation of the Stability of Paraffin/Exfoliated Graphite Nanoplatelet Composites for Latent Heat Thermal Storage Systems.” Journal of Materials Chemistry. Oct 2012.
Building Energy Systems Modeling
A computational/modeling approach is being taken to investigate the performance of buildings in decentralized, microgrid environments. The end goal is to optimize the mix of energy sources and demands shown in Figure 3 to ultimately minimize the amount of energy being consumed. Several solutions are being investigated to achieve this goal. On the supply side, the integration of sustainable energy systems such as wind, solar photovoltaic, and battery technologies are being studied. Space conditioning and lighting systems account for the largest percentage of building energy demand. Energy efficient alternatives to conventional HVAC systems and the use of solid state lighting and plasma lighting technologies are being explored.
As seen in Figure 4, building energy performance is largely dependent on climate conditions. It is important to appropriately select building technologies to reflect their performance in various climatic conditions. System performance evaluation in various weather conditions is facilitated through a computational platform comprising of EnergyPlus and other codes.
These efforts are leveraged through research collaborations across academia, government, and industry. Validation of the models is being facilitated through interactions with Oak Ridge National Laboratory, National Renewable Energy Laboratory, and Lawerence Berkeley National Laboratory where advanced energy efficient building technologies are being developed and for permanent and off-grid systems (Figure 5). The approach is to model structures, test under controlled conditions, and verify with real occupied systems. This work has real world implications in several settings including military, disaster relief, and humanitarian efforts in addition to residential settings.